1. Field of the Invention
This invention relates to semiconductor elements such as semiconductor lasers used in optical communication apparatuses, and in particular, to packages for storing thermoelectric modules performing temperature controls on semiconductor elements.
2. Description of the Related Art
Recently, there are increasing needs for performing high-speed communications of large amounts of data or information as technologies regarding network systems such as the Internet have been rapidly developed and spread worldwide. Large amounts of data or information can be transmitted at a high speed by way of existing optical fiber networks, which are rapidly expanded and are frequently used in recent years. That is, so-called broadband optical networking technologies such as wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) are adapted to multiplexing over channels with respect to optical signals or beams transmitted via a single optical fiber. This realizes high-speed bidirectional communications of large amounts of data or information.
Normally, data or information transmitted over optical fibers are signals that are produced by modulating laser beams, which are radiated (or emitted) from so-called optical semiconductor modules, i.e., electronic devices storing semiconductor lasers. In addition, optical semiconductor modules are also used in optical amplifiers that amplify intensities of signals at intermediate points in transmissions of data or information using optical fibers. Oscillation wavelengths of semiconductor lasers may be greatly affected by temperature; therefore, it is essential to strictly control the temperature of semiconductor lasers during operation. For temperature control, it is possible to use thermoelectric modules or thermoelectric coolers (TEC), which may incorporate numerous Peltier elements.
Containers storing electronic components such as semiconductor lasers and thermoelectric coolers are generally called packages, an example of which is shown in FIG. 21 and FIGS. 22A and 22B, wherein FIG. 21 shows essential parts for assembling a package, and FIGS. 22A and 22B show assembled states of the package. That is, an optical semiconductor module package 60 is mainly constituted by a frame 61, a window holder 62, a base 63, a seal ring 64, ceramic field through members 65, a pair of leads 66, and a cover (not shown). Herein, the frame 61, base 63, ceramic field through members 65, leads 66, and seal ring 64 together with brazing (or soldering) materials (not shown) are combined together as shown in FIG. 22A and are subjected to a heating process.
Thus, the window holder 62 is brazed to one side wall of the frame 61, and the base 63 is fixed to the lower surface of the frame 61 as a base plate by brazing. In addition, a pair of the ceramic field through members 65 are fixed to cutout portions formed on opposite side walls of the frame 61 by brazing. Furthermore, a pair of the leads 66 are attached onto the ceramic field through members 65 by brazing, and the seal ring 64 is brazed onto the ceramic field through members 65 and the frame 61. Then, an electronic component such as a thermoelectric cooler 67 and a semiconductor laser (not shown), or an optical system, is installed and stored in the frame 61, which is then placed in an atmosphere of nitrogen gas. Thereafter, the cover (not shown) is welded onto the seal ring 64, so that the package 60 is formed. Thus, it is possible to produce an optical semiconductor module.
In the above, the ceramic field through members 65 are formed using ceramic materials having wires 65a. Specifically, green sheets composed of aluminum oxide (Al2O3) and binders are formed in prescribed shapes, on which prescribed wires are sintered. Herein, the thermoelectric cooler 67 is arranged between the semiconductor laser and the base 63, so that heat generated by the semiconductor laser is actively radiated (or emitted) outside. Therefore, the base 63 is made of a prescribed material (e.g., CuW) having high thermal conduction. In addition, both the frame 61 and the window holder 62 are made of prescribed materials having small coefficients of thermal expansion, such as iron-nickel-cobalt (FeNiCo) alloy called “Kovar” (trademark).
The aforementioned optical semiconductor module has problems in that it requires a relatively large number of parts, each of which should be specifically processed, and expensive materials are therefore required, increasing the overall manufacturing cost thereof. In addition, numerous parts are assembled together by respective brazing at high temperature, which results in a reduction of yield in manufacture. Furthermore, due to troublesome operations performed in high-temperature conditions, it is necessary to use a specific assembling machine that is expensive, which inevitably raises the manufacturing cost of packages.
In addition, there is another problem in that complicated wiring is required in an optical semiconductor module using ceramic field through members. Furthermore, a heatsink is arranged to join the lower surface of a base made of CuW material, by which heat generated by a semiconductor laser is radiated to the outside. This results in a relatively low heat radiation efficiency, and therefore it is difficult to rapidly radiate heat to the outside.